IN a bombshell world exclusive, The ENQUIRER can reveal that MICHAEL DOUGLAS is hiding a shocking gay secret from his wife Catherine Zeta-Jones and millions of fans!

The 68-year-old actor is consumed with guilt over his gay half brother Eric, who was brutalized for years by their father Kirk and shunned by Michael because neither star could deal with his sexuality, say insiders.

“Michael blames himself for not being there for Eric,” said a source. “But he didn’t have the time. He was too busy with his career and marriage – and he’s regretted it ever since.”

Eric led a troubled life and died of a drug overdose in 2004 at age 46. The source says the guilt Michael felt gnawed at him through the years, and that’s what drove the macho actor to take the role of flamboyant gay showman Liberace in the highly touted HBO movie “Behind the Candelabra.”

His sympathetic portrayal of the pianist, who died of AIDS in 1987, is his personal tribute to Eric.

“Michael is haunted by his brother’s death, always asking himself, ‘How could I have saved him?’ ” said the source. “That’s why he took the part of Liberace. He did it for Eric. It’s his way of making amends.”

For years, Michael kept his guilt a secret, even from his actress wife Catherine, said the close source.

“Despite what Catherine may know about the Liberace movie project, Michael has kept hidden from her the true depths of despair he’s bottled up about his agony over Eric,” said a close source. “She has no idea how tor­tured Michael still is over what Eric endured.

“Michael has never been willing to share this gay secret with Catherine. As a Douglas, he’s always kept the stiff upper lip and the family has never been good about admitting emotional weaknesses. She’ll be shocked when she finds out the extent of his grief.”

As The ENQUIRER recently reported, Mi­chael and Catherine have been having marital problems that prompted them to live apart for a while last summer.

Meanwhile, a close family insider told The ENQUIRER: “We all knew that Eric was gay from an early age be­cause his behavior was very effeminate. Other kids picked on him, but he also baited people – particularly his dad Kirk, who he knew was ashamed of him.

“Kirk tried to ‘beat the gayness’ out of him. I’d hear Eric’s screams through the window, and I once walked in­side and saw Kirk hitting Eric at the top of the stairs. We all knew what was going on, and I know Michael felt real bad about it. Along with other members of his family, he felt they didn’t do enough to help Eric.”

Eric opened up about his tortured past in a shocking 2003 interview just nine months before his death. The aspiring actor, whose mother Anne is Kirk’s second wife, talked about how his dad used to beat him, and he said that both Kirk and Michael turned their backs on him when he needed a career boost.

Adding insult to injury, when Eric was just 12 years old, Kirk shipped him off to an expen­sive mental-health center, The Institute of Living in Hartford, Conn. – where Eric said he was raped by two other boys.

Feeling abandoned by his family, Eric’s life quickly fell apart, plunging him into the world of drugs and booze. He tried killing himself at least three times before his fatal overdose.

“I prevented him from committing sui­cide twice,” his best friend Skip E. Lowe told The ENQUIRER in an exclusive in­terview.

“Eric never discussed men with his fam­ily. He was very lonely and couldn’t come to terms with being gay in a family that was always so macho.

“Eric was the black sheep of the family and a deeply troubled man.”

Michael and other family members even­tually tried to help Eric by offering financial support and paying for rehab stays, but it was too little, too late.

“I am so misunderstood by my father and brother – all they want to do is send me to rehab,” Eric told The ENQUIRER in 2001. “There is absolutely no way I can talk to them about being gay.”

One expert believes that Michael was deeply affected by his brother’s heartbreak­ing problems.

“Seeing his father beat his brother for being gay had to have a profound and traumatic effect on Mi­chael, and probably made him question his own sexuality,” said Emmy-winning “Media Psychiatrist” and author Dr. Carole Lieberman.

“The trauma he witnessed as a child might have been the reason he acted out in his first marriage by being unfaithful to his wife (Di­andra). He was even declared a sex addict and had to go to rehab for his addiction in 1992.”

Dr. Lieberman believes that Michael achieved two goals by taking on the Liberace role: “Playing a sympathetic gay character in a positive way instead of a negative one is a way to rebel against what his dad did to his brother, and to stand up for Eric as well.”